1. Field of the Invention
The present invention relates to apparatus for stacking or unstacking trays, and more particularly to stacking or unstacking trays from a receiving station on a tray support platform such as a conveyor.
2. Description of the Prior Art
Various apparatus have been proposed for stacking and/or unstacking articles at an operating station on a conveyor. U.S. Pat. No. 2,550,587 discloses a box stacking apparatus comprising a supporting table and means for moving a box onto the table. Lifting means are provided to engage and lift the box from the table to a position whereat a pair of stack supporting arms engage the box. The lifting means then release the box which remains engaged by the supporting arms. A timing mechanism causes the lifting means to reciprocate unitl a desired number of boxes have been stacked.
U.S. Pat. No. 3,401,808 discloses apparatus for stacking pallets. The disclosed apparatus comprises a conveyor for moving pallets into a magazine. A vertically movable carriage is mounted to each side of the magazine and at least one pallet-supporting arm is pivotally mounted on each of the carriages. The pallet-supporting arms are pivotably movable into and out of engagement with the opposite sides of a pallet. When a first pallet is supplied by the conveyor the pallet-supporting arms pivot to engage the pallet and under the influence of the vertically moving carriages raise the pallet from a conveyor. As a second pallet is supplied to the magazine by the conveyor, the carriages lower the previously engaged first pallet onto this second pallet. The pallet-supporting arms then disengage the first pallet and move downwardly and inwardly to engage the second pallet. The carriages then raise the pallet-supporting arms causing both the first and second pallets to be raised. This sequence of events is continued until as many pallets are stacked as is desired.
U.S. Pat. No. 3,765,546 discloses apparatus for automatically stacking or unstacking relatively heavy containers. A conveyor supplies the containers to the stacking (or unstacking) apparatus. The apparatus comprises a pair of upright posts arranged at opposite sides of the conveyor. Carriages are mounted for vertical travel on the posts and carry levers pivotably movable between a first position for engaging the containers and a second position for disengaging the containers. The carriages move up and down the posts under the influence of a motor. As the containers are supplied in succession to the stacking apparatus, the levers pivot to the first position and engage the first container. The carriages travel vertically and thus the first container is raised above the conveyor. A second container is then positioned underneath the first container and the first container is lowered onto the second container. The levers then pivot to the second position and disengage the first container, and move to a position whereat the levers pivot to the second position and engage the second container. Once again, the carriages move vertically thereby lifting the first and second containers. This processs is repeated until stacking is complete.
U.S. Pat. Nos. 2,251,197, 2,447,959, and 3,858,732 disclose stacking and/or unstacking apparatus comprising raising and/or lowering members operated through linkage means by some form of eccentric cam means.
All of the aforementioned stacking and/or unstacking apparatus are of relatively complicated construction involving many interacting parts taking up considerable space. The attractiveness of a stacking (or unstacking) apparatus is directly related to its simplicity of design and cost of manufacture. Thus it is desirable to have stacking apparatus capable of achieving the stacking or unstacking functions discussed above while not sacrificing simplicity or cost.